My favorutie clipper at the moment is the Wahl Detailer. There are quality issues though, the wire tends to break close to the clipper my last one lasted just over six months before it broke.
 http://www.amazon.co.uk/Wahl-Professional-Detailer/dp/B0012BFMPY/ref=sr_1_1?ie=UTF8&qid=1344514797&sr=8-1

The Wahl Sterling  2
Here is another good clipper for design work, it is more expensive than the detailer and it doesnt cut as close but it is a clipper I use a lot, it is reliable and had the same one for years, I just changed the clipper head a few times (you can buy them on ebay). http://www.amazon.co.uk/Wahl-Sterling-Professional-Barbers-Trimmer/dp/B0012BIV70

The Wahl Tattoo;
 it seems the obvious choice for design work but its not, I think it was made for the home market rather than barbershops. There are reviews here http://www.sallybeauty.com/wahl-trimmer/SBS-785043,default,pd.html
click on the review tab at the bottom left of the screen, the guy that gives a good review says he changed the blades (to the T-outliner blade) and now it works well. Worth a look.